During sustained activity, such as walking, hiking and running, an individual's feet are subjected to large, repetitious ground reaction or impact forces generated in a gait cycle. A runner's foot experiences these ground reaction forces at various points during a typical gait cycle. The runner's gait cycle begins with the heel strike phase, where the initial ground contact at the lateral side of the heel takes place. The heel strike phase lasts until the rest of the foot or shoe contacts the ground, known as the flat foot phase. In the flat foot phase, the runner's weight rolls forward and inward onto the forefoot as the arch collapses, and moves onto the inner and front part of the forefoot where the foot is pushed off the ground and propelled forward. The flat foot phase lasts until the runner's heel lifts, thereby beginning the toe off phase.
In the heel strike and the flat foot phases, the runner's foot typically pronates or supinates, and such pronation or supination will result in lateral movement of the runner's foot, ankle and lower leg. Conventional running shoes attempt to stabilize the runner's foot by providing a foot-encompassing supportive upper and a generally rigid heel cup shaped to snugly receive and control the runner's heel. However, shoes can be hot, especially during prolonged running in high temperatures. While sandals are open and much cooler, conventional open sandals do not have these same stabilizing mechanisms.
It would be desirable to have an open sandal for running and other activities that can provide proper support and cushioning to dissipate impact forces, limit joint motion beyond the natural motion of the foot and preserve the natural forward motion associated with a wearer's natural gait.